General Description

The MAX220–MAX249 family of line drivers/receivers is intended for all EIA/TIA-232E and V.28/V.24 communications interfaces, particularly applications where ±12V is not available.
The MAX225, MAX233, MAX235, and MAX245/MAX246/MAX247 use no external components and are recommended for applications where printed circuit board space is critical.
The MAX220-MAX249 are offered in 26 different packages with temperatures from 0 to +70°C up to -55°C to +125°C. See ordering information table at the end of the data sheet for all package and temperature options.

 

Applications

● Interface Translation
● Multidrop RS-232 Networks
● Portable Diagnostics Equipment

 

Benefits and Features

Saves Board Space
● Integrated Charge Pump Circuitry
• Eliminates the Need for a Bipolar ±12V Supply
• Enables Single Supply Operation from +5V Supply
● Integrated Capacitors (MAX223, MAX233, MAX235, MAX245–MAX247)
Saves Power for Reduced Power Requirements
● 5μW Shutdown Mode

 

Detailed Description

The MAX220–MAX249 contain four sections: dual chargepump DC-DC voltage converters, RS-232 drivers, RS-232 receivers, and receiver and transmitter enable control inputs.

 

Dual Charge-Pump Voltage Converter

The MAX220–MAX249 have two internal charge-pumps that convert +5V to ±10V (unloaded) for RS-232 driver operation. The first converter uses capacitor C1 to double the +5V input to +10V on C3 at the V+ output. The second converter uses capacitor C2 to invert +10V to -10V on C4 at the V- output.
A small amount of power may be drawn from the +10V (V+) and -10V (V-) outputs to power external circuitry (see the Typical Operating Characteristics section), except on the MAX225 and MAX245–MAX247, where these pins are not available. V+ and V- are not regulated, so the output voltage drops with increasing load current. Do not load V+ and V- to a point that violates the minimum ±5V EIA/TIA-232E driver output voltage when sourcing current from V+ and V- to external circuitry.
When using the shutdown feature in the MAX222, MAX225, MAX230, MAX235, MAX236, MAX240, MAX241, and MAX245–MAX249, avoid using V+ and Vto power external circuitry. When these parts are shut down, V- falls to 0V, and V+ falls to +5V. For applications where a +10V external supply is applied to the V+ pin (instead of using the internal charge pump to generate +10V), the C1 capacitor must not be installed and the SHDN pin must be connected to VCC. This is because V+ is internally connected to VCC in shutdown mode.

 

RS-232 Drivers

The typical driver output voltage swing is ±8V when loaded with a nominal 5kΩ RS-232 receiver and VCC = +5V. Output swing is guaranteed to meet the EIA/TIA-232E and V.28 specification, which calls for ±5V minimum driver output levels under worst-case conditions. These include a minimum 3kΩ load, VCC = +4.5V, and maximum operating temperature. Unloaded driver output voltage ranges from (V+ -1.3V) to (V- +0.5V).
Input thresholds are both TTL and CMOS compatible. The inputs of unused drivers can be left unconnected since 400kΩ input pullup resistors to VCC are built in (except for the MAX220). The pullup resistors force the outputs of unused drivers low because all drivers invert. The internal input pullup resistors typically source 12μA, except in shutdown mode where the pullups are disabled. Driver outputs turn off and enter a high-impedance state—where leakage current is typically microamperes (maximum 25μA)—when in shutdown mode, in three-state mode, or when device power is removed. Outputs can be driven to ±15V. The power supply current typically drops to 8μA in shutdown mode. The MAX220 does not have pull up resistors to force the outputs of the unused drivers low. Connect unused inputs to GND or VCC.
The MAX239 has a receiver three-state control line, and the MAX223, MAX225, MAX235, MAX236, MAX240, and MAX241 have both a receiver three-state control line and a low-power shutdown control.